1. Field of the Invention
The present invention relates generally to an apparatus for reproducing information stored on optical record discs, such as digital audio discs or video discs, and more particularly, to a disc information reproducing apparatus which includes a condensation moisture removal capability.
2. Description of the Prior Art
As is well known, in the fields of audio or video apparatus, high density optical record systems such as digital audio disc systems or video disc systems have been developed. In these systems, audio or video information signals are optical-readably stored and disc record medium in the form of analog data or digitized data by a PCM (pulse-code modulation) technique. Optical audio or video disc players are provided for reproducing the information signals stored on the optical record discs. The optical record discs of this type, for example, compact discs (a type of digital audio disc), optical video or image discs and the like are so arranged that digital data intended for high density storing are stored in the form of a pit string. The pit string forms a spiral track or plurality of concentric tracks on one side of the disc. For reproduction, the pit string is read by means of an optical pickup device. In the compact disc, the information normally is stored on a spiral track from an inner region of the disc towards an outer region of the disc.
The optical pickup device is provided with a light source, such as a semiconductor laser, an optical system comprising, for example, a lens, such as an objective lens, a photodetector and actuators. The semiconductor laser generates a laser beam. The optical record disc is projected the laser beam by the optical system and the optical system introduces the laser beam reflected by the optical record disc to the photodetector. The focus actuator controls positioning of the beam on the optical record disc. The objective lens focuses the laser beam on the surface of the optical record disc. The tracking actuator controls the optical system so that the objective lens makes the laser beam follow the track of the pit string.
The optical information reproducing apparatus, for example, a player for reproducing the compact disc as described above, utilizes an optical pickup device to read data stored on the compact disc. The optical pickup device reads out the data from the compact disc as it moves radially from the inner region of the disc to the outer region of the disc as the compact disc rotates at a constant linear velocity (CLV) in relation to the optical pickup device.
The optical pickup devices must have very high performance for the optical systems and the actuators to read out the high density stored data accurately. However, when the temperature of the environment surrounding the compact disc player suddenly changes from a low temperature to a high temperature, condensation moisture occures and various parts of the player mechanism may be covered by condensation moisture. That is, condensation moisture presents on the construction parts of the compact disc player due to a temperature difference between the parts, which are at a relatively low temperature and the new surrounding environment which is at a latively high temperature. For example, condensation moisture presents on the parts of the compact disc player when the player is brought into a warm room from a cold outdoor area.
In this moisture condensating condition, a problem may occure with the player, especially with the optical system and the actuators. For example, condensation moisture presents on an optical element of the optical system, such as the objective lens, severly disturbs the laser beams to be projected on the disc through the optical system. As a result, the optical pickup device may fail to read out the data from the compact disc. When condensation moisture occures in a gap of a bearing portion that movably supports the actuator in the optical pickup device, the condensation moisture may obstruct the lubrication of the bearing portion due to the surface tension of water (condensation moisture). Moreover, condensation moisture can cause rust in the bearing portion and can damage the lubrication of the bearing.
This problem of condensation moisture has been particularly evident in portable type disc players, because the portable players are often carried to places of different temperatures. For example, such players often are carried between indoors and outdoors. The problem of condensation moisture also has been evident in so-called CD-ROM readers (a CD-ROM is a type of compact disc used as a read only memory device for electronic computers and other various control devices). This is because higher accuracy is required in the reading of the CD-ROMs.
In conventional optical disc information reproducing apparatus, the apparatus has been left as it be until the apparatus has become able to operate. That is, there has been no attempt for positively removing condensation moisture in the apparatus. Then, the inventor of this invention has attempted to use a heater in the optical piockup device for removing condensation moisture from the optical system, especially, the objective lens or the bearing portion of the actuators by its heating energy. However, the use of the heater has made the structure of the optical pickup device much more complicated. The use of the heater also has made the optical pickup device larger and heavier. In addition, additional electric wirings have been necessary between the device and other parts of the compact disc player when a heater has been used so that the structure of the compact disc player has become more and more complicated.